78 REPOET OF COMMISSIONER OF FISH AND FISHERIES. [76] 



expansibility of sea- water made bj Prof. J. S. Hubbard, U. S. N, Col- 

 umn II contains a reduction for temperature of salinometer readings to 

 the standard of 60° Fahr. To facilitate the use of this table the follow- 

 ing directions are given : 



"Eecord the actual observation of hydrometer and thermometer. 

 From column II (which is applicable to any degree of saltness within the 

 given limits) take the number corresponding to the observed tempera- 

 ture and multiply this number by the number of degrees and fractions 

 of a degree that the observed temperature differs from 60°. Apply 

 this product as a correction, with proper sign, to the reading of the 

 salinometer, and the result will be the reading of the salinometer at the 

 standard temperature of 60° Fahr. 



"Example. — Actual reading of thermometer =80o.5; actual reading 

 of salinometer=1.02425. 



"Opposite 80.05 in column II is +0.0001585, which, multiplied by 20.5, 

 gives as a product -f 0.003249. Add this to the observed reading of 

 salinometer, and 1.02750 will result as the reading of the salinometer at 

 the standard temperature. 



"A method quite different in practice for determining the density of 

 sea-water has been suggested by Prof. Wolcott Gibbs, of Harvard Uni- 

 versity. It depends upon the determination of the index of refraction 

 by means of an angular instrument similar to the sextant. As all navi- 

 gators are familiar with the use of the sextant, and as the observation 

 can be made without hindrance from the motion of the ship, this form 

 of th(? instrument may be found to possess certain advantages. 



"KoTE IN 1876. — When the table of reductions for temperature above 

 given was constructed, the investigations relative to the same subject 

 made by Thorpe and Eiicker (Royal Society's Proceedings, January, 1870) 

 were not known. The following comparison of the results of the experi- 

 ments on the thermal dilation of sea-water, as taken from Professor 

 Hubbard's tables, and as derived from the results of Tliorpe and Paicker, 



